Orthogonal Frequency Division Multiplexing with Equalizer
Swaminathan Duraisamy, Chun-Ta Kung
Overview
• Orthogonal frequency division multiplexing (OFDM)
is a method of encoding digital data on multiple
orthogonal subcarrier frequencies.
Key Features
•
Simulation
PACKET LENGTH
Pilot Symbol Structure
• High spectral efficiency, resistant to multipath fading
channel, reduced Inter-Symbol Interference(ISI),
simplified equalizer and channel estimation,
reasonable complexity and efficient implementation
NUMBER OF SUB-CHANNELS
64
LENGTH OF CYCLIC PREFIX
16
MODULATION SCHEME
BPSK, QPSK, 16-QAM
TRANSMITTER OVERSAMPLE FACTOR
4
TRANSMIT SAMPLE RATE
4MHz
RECEIVER OVERSAMPLE FACTOR
4
RECEIVE SAMPLE RATE
4MHz
TYPES OF CHANNEL
IDEAL/ AWGN/ RAYLEIGH FLAT FADING AND
RAYLEIGH FREQUENCY SELECTIVE FADING
GAUSSIAN NOISE VARIANCE
0.001
RAYLEIGH FADING VARIANCE
1
TRANSMITTER CONSTELLATION (QPSK)
IDEAL CHANNEL
•
512
RECEIVER CONSTELLATION (QPSK)
IDEAL CHANNEL
Schmidt and Cox Algorithm (SCA)
Timing Metric
Moose algorithm
Cox & Schmidl
algorithm
System Design
•
Transmitter
Channel Emulation
• Ideal
• AWGN
• Rayleigh Flat Fading
• Rayleigh Frequency Selective Fading Channel
BIT ERROR RATE vs SNR CURVE (QPSK)
AWGN CHANNEL
LabView and USRP
Receiver
•
OFDM is realized by LabView, which is a system
design platform for visual programming
language and can interface with USRP to
implement various communication systems
BIT ERROR RATE vs SNR CURVE (QPSK)
RAYLEIGH FADING CHANNEL
Implementation on USRP
•
Operating at 2.4GHz,
BPSK/QPSK/16-QAM
Eye diagram